ANF DECREASES ACTIVE SODIUM-TRANSPORT AND INCREASES ALVEOLAR EPITHELIAL PERMEABILITY IN RATS

Previous studies reported that atrial natriuretic factor (ANF) decreas ed lung edema in guinea pigs. To determine whether ANF protects agains t lung edema by increasing active Na+ transport and lung edema clearan ce, ANF (10(-7) M) was instilled into the air spaces (n = 5) or perfus ed through the pulmonary circulation (n = 5) of isolated perfused liqu id-filled rat lungs. These animals were compared with five control rat s and four rats having amiloride (10(-5) M) instilled into the air spa ce. Amiloride reduced lung edema clearance by 65%, perfused ANF reduce d lung edema clearance by 32%, and instilled ANF did not change edema clearance compared with responses in control rats after 70 min of expe rimental protocol. Passive Ne movement increased by 91% with perfused ANF and by 52% with instilled ANF compared with that in control rats. Albumin flux from the perfusate into the air space increased in ANF-pe rfused lungs compared with control lungs (P < 0.05) but not when ANF o r amiloride was instilled into the air spaces. These results suggest t hat ANF instilled into rat air spaces or perfused through the pulmonar y circulation increases lung epithelial permeability and that ANF perf used through the pulmonary circulation decreases lung edema clearance due to impaired active Ne transport. Conceivably, the previously obser ved protective effect of ANF was due to reduced pressures across the p ulmonary circulation, which resulted in less edema formation.